class MyStack {
    Queue<Integer> qu1;
    Queue<Integer> qu2;   
    public MyStack() {
        qu1=new LinkedList<>();
        qu2=new LinkedList<>();
    }
    
    public void push(int x) {
        if(!qu1.isEmpty()){
            qu1.offer(x);
        }else if(!qu2.isEmpty()){
            qu2.offer(x);
        }else{
            qu1.offer(x);
        }
    }
    
    public int pop() {
        if(empty()){
            return -1;
        }
        if(!qu1.isEmpty()){
            int size=qu1.size();
            for(int i=0;i<size-1;i++){
                int tmp=qu1.poll();
                qu2.offer(tmp);
            }
            return qu1.poll();
        }else{
            int size=qu2.size();
            for(int i=0;i<size-1;i++){
                int tmp=qu2.poll();
                qu1.offer(tmp);
            }
            return qu2.poll();
        }
    }
    
    public int top() {
        if(empty()){
            return -1;
        }
        int tmp=-1;
        if(!qu1.isEmpty()){
            int size=qu1.size();
            for(int i=0;i<size;i++){
                tmp=qu1.poll();
                qu2.offer(tmp);
            }
            return tmp;
        }else{
            int size=qu2.size();
            for(int i=0;i<size;i++){
                tmp=qu2.poll();
                qu1.offer(tmp);
            }
            return tmp;
        }
    }
    
    public boolean empty() {
        return qu1.isEmpty()&&qu2.isEmpty();
    }
}
